The present invention relates toga surfactant composition for emulsion polymerization.
In an emulsion polymerization of unsaturated monomers, such as vinyl monomers or the like, nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers and anionic surfactants such as alkylbenzene sulfonate salts, alkyl sulfate salts, polyoxyethylene alkyl ether sulfate salts, polyoxyethylene alkylphenyl ether sulfate salts, and higher fatty acid salts have been used.
Among them, surfactants having a low critical micelle concentration (hereinafter, called CMC) have been used, because they work effectively even in a small amount. On the other hand, a surfactant having a high CMC is not suitable to use as surfactant for emulsion polymerization. As to the high CMC-having surfactant, its amount being necessary for emulsion polymerization, which exceeds its CMC, is not practical. (A. S. Dunn and W. A. Al-Shahib, Polymer Colloids II, edited by R. M. Fitch, published by Plenum Press, New York, 1980, p619xe2x80x94628).
It is noted that a polyoxyethylene alkyl ether sulfate is used for emulsion polymerization in B. B. Kine and G. H. Ridlick, Surfactants in Chemical/Process Engineering, edited by D. T. Wasan, M. E. Ginn and D. O. Shah, published by Marcel Dekker, New York, 1988, p305-310.
JP-A 57-78936 shows use of a polyoxypropylene alkyl ether sulfate and a polyoxyethylenepolyoxypropylene alkyl ether sulfate for emulsion polymerization.
The properties requested to the surfactants for emulsion polymerization are that stability upon polymerization and mechanical stability of an emulsion are good, that particle size in the emulsion is small showing a low viscosity and that no environmental problem is resulted, and no surfactant which satisfies all of those properties has been available yet.
An object of the present invention is to provide a surfactant composition for emulsion polymerization satisfying all of the above-mentioned properties.
That is, the present invention provides a surfactant composition for emulsion polymerization comprising a compound (a) represented by the formula (I) and having a CMC in the range of from not less than 0.007 mol Lxe2x88x921 to not more than 0.1 mol Lxe2x88x921 and a compound (b) represented by the formula (II) and having a CMC in the range of from not less than 1xc3x9710xe2x88x925 mol Lxe2x88x921 to less than 0.007 mol Lxe2x88x921, as essential components, at the molar ratio of the components (a) to (b) in terms of (a)/(b) being from 5/95 to 75/25:
R1Oxe2x80x94(A1O)mxe2x80x94SO3M1xe2x80x83xe2x80x83(I)
R2Oxe2x80x94(A2O)nxe2x80x94SO3M2xe2x80x83xe2x80x83(II)
(in the formulae, each of R1 and R2 is a monovalent aliphatic hydrocarbon group; each of A1 and A2 is an alkylene group having 2 to 4 carbon atoms; each of m and n shows the average molar number of alkylene oxide added and is a number selected from 1 to 50; each of M1 and M2 is a monovalent cation; and each of plural A1""s and plural A2""s may be same as or different from another of plural A1""s and plural A2""s, given that the number of A1""s is m and the number of A2""s is n.)
It is preferable that the component (a) has a CMC in the range of from not less than 0.01 mol Lxe2x88x921 to not more than 0.06 mol Lxe2x88x921; R1 has 7 to 11 carbon atoms; m is a number selected from 3 to 30; the component (b) has a CMC in the range of from not less than 0.001 mol Lxe2x88x921 to not more than 0.005 mol Lxe2x88x921; R2 has 12 to 16 carbon atoms; n is a number selected from 3 to 30; and that (a)/(b) ranges from 10/90 to 50/50.
Further, the present invention provides, also, a process for emulsion polymerization, polymerizing unsaturated monomer(s) in the presence of the above-mentioned composition and use of the above-mentioned composition as an emulsifier for emulsion polymerization of unsaturated monomer(s).
The component (a) used in the present invention is a compound which is represented by the formula (I) and which has a CMC of in the range of from not less than 0.007 mol Lxe2x88x921 to not more than 0.1 mol Lxe2x88x921, preferably 0.01 to 0.06 mol Lxe2x88x921 and may be used either solely or jointly by combining two or more. Another component (b) is a compound which is represented by the formula (II) and which has a CMC in the range of from not less than 1xc3x9710xe2x88x925 mol Lxe2x88x921 to less than 0.007 mol Lxe2x88x921, preferably from 0.001 to 0.005 mol Lxe2x88x921 and may be used either solely or jointly by combining two or more.
In the present invention, the CMC is a value as measured by means of a conductometric titration.
In the formulae (I) and (II), it is preferable that R1 is a linear or branched alkyl group having 7 to 11 carbon atoms and that R2 is a linear or branched alkyl group having 12 to 24, particularly 12 to 16, carbon atoms. A1 and A2 are preferably ethylene group or propylene group. When two or more kinds of alkylene oxides are added, any of random addition and block addition may be applied. Alternatively, both addition methods may be combined. It is respectively preferable that at least half of A1""s is or are ethylene groups at condition of the half number being m/2 and that at least half of A2""s is or are ethylene groups at condition of the half number being n/2. Then, it is particularly preferable that A1 and A2 are ethylene groups. It is preferable that each of m and n is from 3 to 30. Each of M1 and M2 is preferably an alkaline metal such as sodium and potassium; ammonium; or a protonated amine such as alkanolamine.
The compound represented by the formula (I) or (II) may be manufactured, for example, by adding an alkylene oxide such as ethylene oxide and propylene oxide to an aliphatic monohydric alcohol, then sulfating with a sulfonating agent such as SO3 gas, and neutralizing with NaOH or the like.
The compounding ratio of the components (a) to (b) in the composition of the present invention in terms of a molar ratio of (a)/(b) is from 5/95 to 75/25, preferably from 10/90 to 50/50. When (a)/(b) is less than 5/95, viscosity of the emulsion becomes too high and, in addition, its mechanical stability is not sufficient. On the other hand, when (a)/(b) is more than 75/25, the particle size becomes too big and, in addition, the stability upon polymerization and mechanical stability are not sufficient.
Specific examples of the monomer, which can be subjected to an emulsion polymerization using the surfactant composition of the present invention, include an aromatic vinyl monomer such as styrene, xcex1-methylstyrene and chlorostyrene; an acrylate ester such as methyl acrylate, ethyl acrylate and butyl acrylate; a methacrylate ester such as methyl methacrylate and ethyl methacrylate; a vinyl halide and a vinylidene halide such as vinyl chloride, vinyl bromide and vinylidene chloride; a vinyl ester such as vinyl acetate and vinyl propionate; a nitrile such as acrylonitrile and methacrylonitrile; and a conjugated diene such as butadiene and isoprene. Each of these monomers may be used solely or two or more of them may be used jointly.
It is preferable that the surfactant composition of the present invention is used in the range of 0.1 to 20 parts by weight, particularly 0.5 to 5 parts by weight, per 100 parts by weight of the monomer.
The surfactant composition of the present invention may be used together with a nonionic surfactant such as polyoxyethylene (the molar number of ethylene oxide added being 0 to 100) alkyl or alkenyl (the number of carbon atoms of the alkyl or the alkenyl group being 12 to 24) ether. It is also possible to use a water-soluble protective colloid together.
There is no particular limitation to conditions for the emulsion polymerization using the surfactant composition of the present invention. Preferable amount of the monomer based on the total system is 20 to 70% by weight, particularly 40 to 50% by weight. Incidentally, for the emulsion polymerization of the present invention, may be used any of emulsion polymerization methods such as monomer addition method, batch method and emulsion addition method.
When the surfactant composition of the present invention is used as an emulsifier for an emulsion polymerization, the amount of the coagula generated during the polymerization is small. Namely, the stability upon polymerization is good, the mechanical stability of the obtainable emulsion is also good and the emulsion having the small particle size and the low viscosity is further obtained.